Jim Lillo, engineer-manager of the Bay County Road Commission, said the bridges were closed due to a federal mandate that has been in effect since Jan. 1, 2011.

The Pinconning River near Fraser Road on Wednesday, Jan. 30.Alex Mitchell | MLive.com

The mandate states: "A detour will be in effect for any bridge closed due to the potential undermining threat caused by flood waters at a bridge structure. Due to the sheer number of structures impacted, the detour routes will NOT be signed. Notice will be given to local media outlets 'to refer to the BAY COUNTY ROAD COMMISSION website; www.baycoroad.org' for bridge locations
and recommended detour routes."

The recent rainfall and melting ice and snow led to the flooding, in turn prompting Road Commission personnel to inspect the bridges.

“There’s a line on the bridges and if the water gets above that point, we have to close them,” Lillo said.